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#!/usr/bin/env python3
"""
Reads temperature and humidity from an SI7021 sensor (I2C) and renders
the values to a Waveshare 2.13 inch e-Paper HAT.
The Waveshare EPD library (waveshare_epd) is not bundled in this repo.
See README.md for setup instructions.
"""
import time
from smbus2 import SMBus
from PIL import Image, ImageDraw, ImageFont
from waveshare_epd import epd2in13_V4 # adjust module name for your HAT version
I2C_BUS = 1
I2C_ADDR = 0x40
POLL_INTERVAL = 120 # seconds between display refreshes
def read_si7021(bus: SMBus) -> tuple[float, float]:
"""Return (temp_c, humidity_pct) from the SI7021 sensor."""
rh_raw = bus.read_i2c_block_data(I2C_ADDR, 0xE5, 2) # measure RH, hold master
time.sleep(0.1)
humidity = ((rh_raw[0] * 256 + rh_raw[1]) * 125 / 65536.0) - 6
temp_raw = bus.read_i2c_block_data(I2C_ADDR, 0xE3, 2) # measure temp, hold master
time.sleep(0.1)
temp_c = ((temp_raw[0] * 256 + temp_raw[1]) * 175.72 / 65536.0) - 46.85
return temp_c, humidity
def render(epd: epd2in13_V4.EPD, temp_c: float, humidity: float) -> None:
"""Draw sensor readings on the e-paper display.
The 2.13in HAT is 122×250 px (portrait). We create a landscape image
(250×122) by swapping width/height, which matches the typical Waveshare
example convention of passing (epd.height, epd.width) to Image.new.
"""
image = Image.new("1", (epd.height, epd.width), 255) # 255 = white background
draw = ImageDraw.Draw(image)
font_large = ImageFont.load_default(size=40)
font_small = ImageFont.load_default(size=22)
draw.text((10, 8), f"{temp_c:.1f} \u00b0C", font=font_large, fill=0)
draw.text((10, 62), f"{humidity:.1f} % RH", font=font_small, fill=0)
epd.display(epd.getbuffer(image))
def main() -> None:
epd = epd2in13_V4.EPD()
epd.init()
epd.Clear()
bus = SMBus(I2C_BUS)
try:
while True:
temp_c, humidity = read_si7021(bus)
render(epd, temp_c, humidity)
time.sleep(POLL_INTERVAL)
except KeyboardInterrupt:
epd.sleep()
if __name__ == "__main__":
main()
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